After five years of domestic turmoil marked by angry separations and short-lived reconciliations, a Bronx ex-con fatally shot his pregnant girlfriend and her sister in front of his teen stepdaughters, the terrified girls told neighbors.

Before he fled, Edelmiro “Junior” Cesare, 30, threatened to kill one of the girls as she knelt sobbing over her mother’s body, the teens told neighbors after the Tuesday night shooting.

Police yesterday were combing the city for Cesare, whom they described as a “person of interest” in the case. They said he had a police record, but offered no details.

Neighbors said they saw Cesare flee the building at 187 Throgs Neck Blvd. about 10:30 p.m., leaving his daughter, Maya, 4, and stepdaughters, Christine, 13, and Ashley, 15, with the bodies of their mother, Loreen Merchan, and aunt, Yasmin Merchan.

The couple’s 2-year-old daughter was with her grandmother in Waterbury, Conn., sources said.

Cesare had been living in the building with Loreen Merchan, 33, for the past two weeks, neighbors said. It was just the latest reconciliation.

But Sunday, when friend and neighbor Deyanira Vazquez last saw 4-months- pregnant Loreen and Yasmin, 26, she learned “they had been fighting again.”

And Tuesday morning, she said, Cesare told the landlord he was moving out.

Hours later, neighbors heard eight gunshots, followed by screams, from the couple’s apartment.

Vazquez said her husband looked outside and “saw Junior running out of the building.”

Inside the apartment, the two sisters were sprawled on the floor with the two teens bent over them, crying and soaked in blood, Vazquez said.